To achieve stable operation of whispering gallery mode (WGM) resonator-based lasers, the stabilization of the frequency of its optical resonator is necessary. However, the frequency of such lasers can vary as a result of temperature changes of the optical resonator and its surroundings. In order to stabilize the frequency of optical resonators, it is known to compare their frequency and temperature with the frequency and temperature of an external etalon. However, such a comparison requires the stabilization of the frequency and temperature of the external etalon which can be very difficult and in effect just passes the problem on to the external etalon.
Accordingly, there exists a need for a simple and efficient system for precisely measuring the temperature shift or temperature differential of an optical resonator.